1. Field of the Invention
The present invention relates to an electronic part such as a capacitor, a varistor, or an inductor, and, more specifically, to an electronic part having a configuration provided with a metallic external terminal arranged to alleviate any stress caused by a substrate upon which the part is mounted.
2. Description of the Related Art
Some large size ceramic electronic parts such as a chip type multi-layer ceramic capacitor to be used for an application requiring a large capacity, have a configuration provided with an external terminal comprising a metallic plate used as the external terminal for alleviating the stress derived from the deflection of the substrate upon which the part is mounted.
For example, FIG. 9 and FIG. 10 show electronic parts (multi-layer ceramic capacitors) which are formed by installing an external terminal 55 in a multi-layer member 52 comprising a plurality of laminated multi-layer ceramic capacitor elements 51 provided with electrodes 53 at both end faces so as to connect with each terminal 55 via a jointing material 54 such as a solder and a conductive adhesive.
In the multi-layer ceramic capacitor of FIG. 9, an external terminal 55 having a flat plate-like shape with the lower end part bent around the lower surface side of the multi-layer member 52 is used. In the multi-layer ceramic capacitor of FIG. 10, a cap-like external terminal 55 having a flat plate-like shape with the peripheral part bent so as to fit into the end part of the element multi-layer member 52 is used.
However, in the above-mentioned electronic parts using an external terminal comprising a metallic plate, a problem is involved in that if a thermal impact is applied in mounting the part to a substrate, due to deflection of the substrate or the difference between the multi-layer ceramic capacitor element and the external terminal in terms of the coefficient of linear expansion, tensile stress is applied on the multi-layer ceramic capacitor element so as to facilitate generation of crack or peel-off.
The object of the present invention is to solve the above-mentioned problem, and to do so by providing a highly reliable electronic part capable of restraining or preventing generation of crack, split or peel-off in an electronic part element of which the electronic part is comprised by reducing the stress to be applied onto the electronic part element when thermal shock is applied.
In order to achieve the above-mentioned object, an electronic part according to a first aspect of the present invention comprises an electronic part element, and an external terminal made of a metallic plate provided with a slit attached to the electronic part element via a conductive jointing material.
In the present invention, a solder, a conductive adhesive, or the like, can be used as the conductive jointing material.
Moreover, in the present invention, since only a slit is formed in the external terminal and thus the contacting area of the external terminal and the electronic part element is almost the same as the case without forming the slit, it will not lead to an increase of the ESR (Equivalent Series Resistance).
Moreover, an electronic part according to a second aspect of the present invention comprises a multi-layer member with a plurality of laminated electronic part elements, and an external terminal made of a metallic plate provided with a slit, attached to the element multi-layer member via a conductive jointing material.
In an electronic part according to a third aspect of the present invention, the slit of the external terminal is formed in the direction substantially perpendicular to the mounting surface of the electronic part.
Moreover, in an electronic part according to a fourth aspect of the present invention, a plurality of slits are provided in the metallic plate comprising the external terminal.
By providing one or more of a plurality of slits as in the first, second or fourth aspects or a perpendicular slit as in the third aspect, the stress to be applied onto the electronic part element generated by the deflection of a substrate upon which the electronic is to be mounted or the difference between the external terminal and the electronic part element in terms of the coefficient of linear expansion when thermal shock is applied can be alleviated efficiently.
Moreover, in an electronic part according to a fifth aspect of the present invention, the slit is filled with a substance having a larger coefficient of linear expansion or a substance having a lower Young""s modulus with respect to the material comprising the external terminal.
In the case of the fifth aspect, the stress to be applied onto the electronic part element can be reduced because the substance for filling the slit expands and contracts more dramatically than the external terminal. More particularly, the filling substance contracts more dramatically than the external terminal at a low temperature, and, accordingly, the deformation (expansion, contraction) of the external terminal is restrained, that is, the expansion and contraction of the external terminal itself are restrained owing to the influence from the expansion and the contraction of the filled substance, and consequently the stress to be applied onto the electronic part element is reduced. Moreover, when a substance having a lower Young""s modulus with respect to the external terminal is provided for filling the slit, the stress on the electronic part itself becomes smaller.
In the electronic part according to the fifth aspect, it is preferable that the filing material is accommodated in the slit, but even if it overflows the slit slightly, it does not cast a great influence on the effect of restraining the stress to be applied onto the electronic part element.
The present inventors presumed that there is a risk of lowering the effect of absorbing or alleviating the stress if the slit formed in the external terminal is filled with the jointing material (such as a solder and a conductive adhesive) for jointing the external terminal with the electronic part element, however in reality, it was leaned that the stress to be applied onto the electronic part element can be reduced by filling with a substance having a larger coefficient of linear expansion or a substance having a lower Young""s modulus with respect to the material comprising the external terminal.
As a substance having a larger coefficient of linear expansion or a substance having a lower Young""s modulus with respect to the material comprising the external terminal for filling the slit, various substances can be used, but the stress to be applied onto the electronic part element can be restrained efficiently in accordance with a sixth aspect of the invention by using at least one selected from the group consisting of a resin, a solder and a conductive adhesive.
In an electronic part according to a seventh aspect, the substance for filling the slit is the substance which is the same as the jointing material used for jointing the external terminal with the electronic part element.
By using a substance which is the same as the jointing material used for jointing the external terminal with the electronic part element as the substance for filling the slit, the slit can be filled efficiently with a substance having a larger coefficient of linear expansion or a substance having a lower Young""s modulus with respect to the material comprising the external terminal so that the present invention can further be effective while avoiding the complication of the production process.
As the jointing material used for jointing the external terminal and the electronic part element, a substance having conductivity, such as a solder and a conductive adhesive is mainly used, but a resin not having conductivity can also be used, aiming only at the mechanical connection but not the electrical conduction. Filling the slit of the external terminal with such a resin also corresponds to the embodiment of the seventh aspect.
Moreover, in an electronic part according to an eighth aspect of the present invention, an electronic part according to any of the first to seventh aspects is accommodated in an insulated case with a part of the external terminal arranged so as to be connectable with an external object.
In the case of an electronic part with a case, accommodating an electronic part comprising an external terminal made of a metallic plate provided with a slit in an insulated case, generation of crack or split in the electronic part element can be prevented efficiently by alleviating the stress to be applied onto the electronic part element generated by the deflection of the mounted substrate or the difference between the external terminal and the electronic part element in terms of the coefficient of linear expansion when the thermal shock is applied as well as breakage or electric shock caused by stress from the outside, in particular, by any striking of the case can be prevented.
Moreover, in an electronic part according to a ninth aspect of the present invention, an electronic part according to any of the first to seventh aspects is accommodated in an insulated case with the insulated case filled with a resin with a part of the external terminal exposed.
In the case where an electronic part using an external terminal made of a metallic plate provided with a slit is accommodated in an insulated case and the insulated case is filled with a resin, an effect which is the same as the effect achieved in the case of the electronic part according to the eighth aspect as can be achieved as well. More particularly, since the electronic part element is embedded and maintained in the resin, the impact resistance, the vibration resistance, and the weathering resistance can further be improved. Moreover, the resin for filling the inside of the case can also serves as the substance for filling the slit.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.